Tweco 150XL CE PAK Master - Manuel (Page 25)

Manual 0-2826 3-7 INSTALLATION
5. Make sure work cable and ground cables are properly con-
nected. The work cable must have a solid connection to the
cutting table. The work and ground connections must be
free from rust, dirt, grease, oil and paint. If necessary grind
or sand down to bare metal. Use lock washers to keep the
connections tight. Using electrical joint compound to pre-
vent corrosion is also recommended.
6. The plasma power supply chassis is connected to the power
distribution system ground as required by electrical codes.
If the plasma supply is close to the cutting table (see NOTE)
a second ground rod is not usually needed, in fact it could
be detrimental as it can set up ground loop currents that
cause interference.
When the plasma power supply is far away from the
ground rod and interference is experienced, it may help
to install a second earth ground rod next to the plasma
power supply. The plasma power supply chassis
would then be connected to this ground rod.
NOTE
It is recommended that the Plasma Power Supply be
within 20 - 30 ft (6.1 – 9.1 m) of the cutting table, if
possible.
7. The plasma control cable should be shielded with the
shield connected only at the cutting machine end.
Connecting the shield at both ends will allow ground
loop currents which may cause more interference than
with no shield at all.
C. Creating An Earth Ground
1. To create a solid, low resistance, earth ground, drive a
1/2 in (12 mm) or greater diameter copper clad ground
rod at least 6 - 8 ft (1.8 - 2.4 m) into the earth so that the
rod contacts moist soil over most of its length. Depend-
ing on location, a greater depth may be required to
obtain a low resistance ground (see NOTE). Ground
rods, typically 10 ft (3.0 m) long, may be welded end to
end for greater lengths. Locate the rod as close as pos-
sible to the work table. Install a ground wire, 1/0
AWG (European 50 mm
2 ) or greater, between the
ground rod and the star ground point on the cutting
table.
NOTE
Ideally, a properly installed ground rod will have a
resistance of three ohms or less.
To test for a proper earth ground, refer to the following
diagram. Ideally, the reading on the multimeter should
be as follows:
• For 115VAC: 3.0 VAC
• For 230VAC: 1.5 VAC
Art # A-02971
+
_
Meter set to
VAC setting
Neutral
Line (Hot)
100W
Light Bulb
115 or 230VAC
WARNING
Use extreme caution. This
test uses live voltage.
115VAC: 3.0 VAC
230VAC: 1.5 VAC
V ~
V
~
VR COM A
Ground
Rod
Ground Testing
CAUTION
No other connections should be made at the
ground rod being tested. This test assumes that
the 115 or 230-VAC source neutral is connected
to the utility earth ground.
2. Increasing the ground rod length beyond 20 - 30 ft (6.1 – 9.1
m) does not generally increase the effectiveness of the
ground rod. A larger diameter rod which has more surface
area may help. Sometimes keeping the soil around the
ground rod moist by continuously running a small amount
of water into it will work. Adding salt to the soil by soaking
it in salt water may also reduce its resistance. When these
methods are used, periodic checking of the ground resis-
tance is required to make sure the ground is still good.